Traumatic events and chronic stress have been implicated in the development of stress-related psychopathologies. Most animal models of stress-related disorders use tightly controlled, but artificial stressors, and it is critical to extend these to more natural relevant stressors. Social stress is a more natural stressor and can suppress reproductive function (e.g. lack of courtship behavior, delayed gonadal function, or delayed onset of puberty) in animals of low social status or those exposed to chronic social stress. These studies look at the role of neurotrophins in social status and how a brief interaction can cause a long term change in behavior. They also investigate the neural effects of chronic social stress. Neurotrophins have altered expression in different pathologies such as epilepsy, Alzheimer's and Parkinson's diseases, and depression. Particularly in its association with forms of depression, social defeat may provide insights into the mechanisms by which these neurotrophin levels are related to depression. The results obtained will provide a foundation for developing an integrative model that can be applied across taxa. The fundamental goal of this proposal is to design and implement experiments that will facilitate my training as a developing molecular neuroendocrinologist and elucidate the mechanisms underlying socially- mediated modifications in social status behavior. The general research objectives are to: 1) characterize the relationship between neurotrophins and dominant and subordinate status, 2) test hypotheses related to the role of neurotrophins in the acquisition and maintenance of social status and its related behavior. Specifically, I propose two inter-related studies: 1) status-dependent differences in aggression, submissive behavior, plasma corticosterone concentrations, and neurotrophin brain mRNA expression and the relationships of these factors will be investigated, 2) direct experimental manipulations will assess the role of neurotrophins in the acquisition, consolidation, and maintenance of social status and its related behavior. These studies will aid in understanding a fundamental process by which social stress can induce persistent changes in the brain, such as is seen in patients with post-traumatic stress disorder and other mental health conditions that are exacerbated by social stress or helped by successful social interactions.